linux-kernel - Re: [RFC PATCH v3 04/19] KVM: x86: mmu: allow to enable write tracking externally

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Date:   Sun, 22 May 2022 13:22:05 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        intel-gfx@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Brijesh Singh <brijesh.singh@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
        intel-gvt-dev@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH v3 04/19] KVM: x86: mmu: allow to enable write
 tracking externally

On Thu, 2022-05-19 at 16:37 +0000, Sean Christopherson wrote:
> On Wed, Apr 27, 2022, Maxim Levitsky wrote:
> > @@ -5753,6 +5752,10 @@ int kvm_mmu_init_vm(struct kvm *kvm)
> >  	node->track_write = kvm_mmu_pte_write;
> >  	node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
> >  	kvm_page_track_register_notifier(kvm, node);
> 
> Can you add a patch to move this call to kvm_page_track_register_notifier() into
> mmu_enable_write_tracking(), and simultaneously add a WARN in the register path
> that page tracking is enabled?
> 
> Oh, actually, a better idea. Add an inner __kvm_page_track_register_notifier()
> that is not exported and thus used only by KVM, invoke mmu_enable_write_tracking()
> from the exported kvm_page_track_register_notifier(), and then do the above.
> That will require modifying KVMGT and KVM in a single patch, but that's ok.
> 
> That will avoid any possibility of an external user failing to enabling tracking
> before registering its notifier, and also avoids bikeshedding over what to do with
> the one-line wrapper to enable tracking.
> 

This is a good idea as well, especially looking at kvmgt and seeing that
it registers the page track notifier, when the vGPU is opened.

I'll do this in the next series.

Thanks for the review!

Best regards,
	Maxim Levitsky